Liquid electrolytes obtained by dissolving an electrolyte salt in a solvent have been used heretofore to provide ion conductivity between electrodes in electrochemical devices such as secondary cells, fuel cells, dye-sensitized solar cells and actuators. However, liquid electrolytes comprising a solvent involve a risk of reduction in the liquid volume with time because of volatilization of the solvent, or a risk of liquid leakage. Therefore, development of alternatives to such electrolytes has been studied.
As for electrolytes alternative to liquid electrolytes comprising a solvent, use of nonvolatile ionic liquids has been studied. For example, an electrolyte composition comprising an imidazolium or pyridinium compound substituted with an oligoether group has been proposed in Patent Document 1. Use of such an ionic liquid as an electrolyte ameliorates the problem of reduction in the liquid volume with time because of volatilization of the solvent and the problem of liquid leakage which are observed in liquid electrolytes comprising solvents. However, since this technology still uses a liquid as an electrolyte, it cannot completely solve a problem of complicated manipulations in the production of electrochemical devices and liquid leakage during use of the devices.
Therefore, use of a polymer material having superior ion conductivity as an electrolyte (so-called a polymer electrolyte) has been studied. For example, use for an electrolyte composition of a polyether compound comprising a polyalkylene oxide main chain, an ionic side chain and a counter ion for the ionic side chain, in which the ionic side chain or the counter ion exhibits liquid crystal properties, has been proposed in Patent Document 2. Furthermore, a solid electrolyte composition comprising a polymer compound which has a cation structure in the main chain or side chains and which has a halide or polyhalide ion as a counter anion for the cation structure has been proposed in Patent Document 3.
Since these electrolyte compositions are solid and hardly exhibit fluidity under ordinary use environments of electrolytes, the problem of leakage of the liquid during use of electrochemical devices is solved.
However, there was a problem that, because the electrolyte compositions described in Patent Documents 2 and 3 are solid, they are inflexible in being applied to electrochemical devices as electrolytes and they are hard, for example, to coat on or impregnate into other materials. Meanwhile, there was another problem that, since these electrolyte compositions have random structures, they were easily affected by media such as organic solvents or water.
Therefore, there has strongly been sought a material which can provide electrolytes having superior processability enough to be coated on or impregnated into other materials, also having resistance to organic solvents, water, etc., and exhibiting, after being processed, superior shape-retaining properties enough to be prevented from liquid leakage, swelling, elution, etc.